It is well known that the direction of magnetization of a magnetic material can be reversed or switched by impressing an external magnetic field of opposite polarity upon the material. Typically, magnetic material may be placed upon a nonmagnetic substrate and then divided or separated by a grid-like pattern to create magnetic post elements. When electronic conductors are placed within the separations which form the gird-like pattern, electric currents may be passed through the conductors to generate a magnetic flux about each conductor. This flux is concentrated at the intersection of two conductors in two of the four quadrants formed by the intersection. Through the utilization of a low anisotropy material located within one of the two quadrants in which the flux is concentrated, it is possible to control which magnetic post element will be switched at each intersection.
The concept of placing a low anisotropy material within the high anisotropy material of a magnetic post element has been disclosed in a co-pending patent application, Ser. No. 320,819, filed Nov. 12, 1981, by Bruce E. MacNeal and William E. Ross, entitled "Altering The Switching Threshold Of A Magnetic Material," assigned to the same assignee as the present invention. In yet another co-pending application, the concept of increasing the density of the magnetic post elements by dividing the post elements along their diagonals has been discussed. See co-pending patent application Ser. No. 375,327, filed May 5, 1982, by William E. Ross entitled "Method And Device For Increasing The Density Of A Plurality Of Switchable Magnetic Elements."
The MacNeal and Ross patent applications mentioned above do not provide for redundancy within the magnetic system in the event that a magnetic post element should become defective due to early switching characteristics. Other defects might include optical defects within a magnetic post, reduced current sensitivity within a magnetic post which would prevent its switching, electrical shorts, and open-electrical conductors.